Functionalized polyolefin (FPO) materials have potential usefulness for a number of commercial applications. Polyolefins which are reactive or polar can, for example, provide products for major applications, such as high temperature elastomers resistant to oil, and can also provide structural polyolefins. Polyolefins in the form of oil resistant elastomers could compete with chloroprene and nitrile rubber in oil resistant applications but could offer better high temperature performance and service life than ethylene-propylene diene rubbers at a comparable price. Structural polyolefins could be low cost polymeric materials with improved stiffness, strength and use temperatures that would extend the boundary of polyolefins to structural applications, for example, to uses within the automotive area.
Post-polymerization functionalization requires synthesis of precursor olefin copolymers which carry functionalizable “reactive hooks”, such as residual double bonds or aromatic rings. Such “reactive hooks” can then be appropriately functionalized using various chemistries.
The present invention concerns utilization of functionalizable copolymer precursors which contain reactive hooks in the form of residual double bonds. Copolymer precursor materials of this type are realized by incorporating a diene co-monomer into the copolymers that can subsequently be functionalized. One of the double bonds in the diene comonomer permits co-polymerization of this co-monomer with one or more α-olefins. The remaining unreacted double bond in each of the pendent co-monomer moieties along the polymer chain is then available for conversion to selected polar groups via a separate process, generally in a different reactor.
This olefin-diene approach allows production of a wide range of products using a single technology. Functionalization of the diene co-monomers within the copolymer precursor permits the introduction of polarity for oil resistance and can also improve the thermal and chemical stability characteristics of the resulting functionalized copolymer materials. Further, glass transition temperature, Tg, of the resulting functionalized copolymer can be adjusted by both the choice and content of the diene co-monomer.
One type of known functionalization of olefin/diene copolymers involves reaction of the copolymer precursor material with an oxidizing agent to provide an epoxidized material having oxirane groups formed at the sites of the residual double bonds within the copolymer precursor. Epoxidation of unsaturated materials is a stereospecific reaction, and the rate of epoxidation is governed by the substitutents on the double bond.
Epoxidation of olefin/diene copolymers can be effected by the use of various peroxides and peracids. In the use of peracids, there are two possible procedures, viz., either the peracid is present throughout the reaction or alternatively the peracid is prepared in situ during the reaction. Performic acid prepared in-situ, such as from formic acid and hydrogen peroxide, is very effective as an epoxidizing agent and can be used without catalyst.
While peracid-based epoxidation is effective, there can be environmental and safety concerns associated with the use of peracids. Catalytic epoxidation alternatives using hydrogen peroxide as an oxidizing agent instead of peracids can be used to epoxidize some unsaturated materials. Catalysts based on the use of high valent (do), mostly Ti, V, Mo, W, and Re, metal complexes are known to promote alkene epoxidation with H2O2. Some notable effective epoxidation catalysts for use with hydrogen peroxide include titanium silicates, peroxophosphotungstates, manganese triazocyclononane, and methylrhenium trioxide.
As an alternative to peracid-based epoxidation, the catalytic electrophilic activation of hydrogen peroxide with transition metal compounds for the epoxidation reaction of alkenes has, in fact, become a matter of significant interest. And there are a few examples in the art of catalytic oxidation being used to introduce epoxy groups into copolymers containing relatively low levels of unsaturation or unsaturation which is primarily found within the copolymer backbone.
Epoxidation of copolymers having higher levels of pendent unsaturated co-monomers is more difficult than functionalization of non-polymeric alkenes or other types of unsaturated polymers, either with or without use of peracid oxidizing agents or epoxidation catalysts. Such functionalizable copolymers with higher levels of diene-based comonomers have enhanced potential for side reactions and cross-linking which can be brought about by the presence of greater amounts of organic peracids used as epoxidizing agents. Use of an epoxidation catalyst can eliminate the need for the presence of large amounts of acidic reagents and can permit the use of a hydrogen peroxide oxidizing agent instead. But the presence of a metal catalyst can also promote crosslinking or side reactions of the diene-containing copolymer and/or can also potentially degrade the hydrogen peroxide oxidizing agent which is being used along with the catalyst.
Epoxidation of a broad variety of alkenes, including olefin/diene copolymers, is in general known in the art. Representative prior art showing various procedures for epoxidizing a number of types of unsaturated materials includes Hafren et al., Macromol. Rapid Commun., Vol. 26, pp. 82-86 (2005); Song et al., J. Polym. Sci. Polym. Chem., Vol. 40, pp. 1484-1497 (2002); Shigenobu et al. (Maruzen Petrochemical); Japanese Patent Appln. No. JP2001-031716A, published Feb. 26, 2001; Suzuki et al., Journal of Applied Polymer Science, Vol. 72, pp. 103-108 (1999); and Li et al.; Macromolecules, Vol. 38, pp. 6767-6769 (2005).
Epoxidation of non-polymeric materials using catalysts or selected reaction medium solvents is also in general known in the art. Representative prior art references showing these kinds of expoxidation includes Herrmann et al., Angew. Chem. Int. Ed. Engl. Vol. 30, No. 12, pp. 1638-1641 (1991); Van Vliet et al., Chem. Commun., pp. 821-822, (1999); and Neimann et al., Org. Letters, Vol. 2, No. 18, pp. 2861-2863 (2000).
Given the actual and potential usefulness of functionalized olefin/diene copolymers—and especially those functionalized by epoxidation—for a variety of commercial applications, it would be desirable to identify especially effective and efficient processes for preparing such epoxidized copolymer materials. Such processes would use relatively mild epoxidation reaction conditions and relatively inexpensive and readily available reaction mixture adjuvants such as reaction solvents. And such processes would desirably be carried out without the need for potentially troublesome peracid oxidizing agents or metal-based epoxidation reaction catalysts.